1. Field of the Invention
The present invention relates in particular to data transmission networks using optical fibers.
2. Description of the Prior Art
Each node of a network of the above kind using optical fibers receives signals that come in particular from other nodes on the same network. The signals are optical signals, i.e. they are conveyed by optical waves, and are referred hereinafter as “input” signals. Likewise, the node sends, in particular to other nodes, other signals of the above kind that are referred to hereinafter as “output” signals. The output signals are equivalent to respective input signals in the sense that they convey the same data, but they may be in a different order and their carrier wavelengths may be different. Correspondences must be established between, on one hand, the sources from which the input signals come and, on the other hand, the destinations to which the equivalent output signals must be sent.
In networks that use asynchronous transmission, for example those which use prior art protocols such as the Asynchronous Transfer Mode (ATM) and the Internet Protocol (IP), the signals to be transmitted take the form of packets. Said correspondences to be established are then made by a management unit or controller included in the node for this purpose, and in this case the node is referred to as a router. The data that it is necessary for the router to have in order to fulfill its function is supplied to it in particular by labels that are specific to the respective packets and which can be included in packet headers, for example, or conveyed by waves allocated to that function.
The above kind of router has, on the-one hand, input ports via which it receives packets and, on the other hand, output ports via which it transmits packets equivalent to the input packets. The number of output ports is typically the same as the number of input ports. A “capacity” of the router is defined. It consists of the product of the number of input ports by the data bit rate that can be transmitted by the router via each of those ports. To convey the packets between its input ports and its output ports the router uses carrier waves whose wavelengths constitute operating wavelengths of the router. To select a path, and possibly a path duration, for each packet between an input port and an output port, it includes switches that usually consist of semiconductor optical amplifiers.
When implementing a transmission network using the above kind of router, it is desirable fir the number of users that can use the network to be as large as possible, and the same applies to the data bit rate that can be transmitted between the users. To this end it is desirable for the capacity of the routers included in the network to be increased. However, increasing the capacity of the above type of prior art router necessitates an equivalent increase in the number of operating wavelengths of the router and therefore in the number of carrier wavelengths received by each of its optical switches. In the above kind of switch, increasing the latter number can lead to four-wave mixing, causing optical crosstalk. The number of the above kind of switches is also necessarily increased. The increase in the capacity of the router is then limited both by the risk of optical crosstalk and by the cost of implementing the router and in particular the cost of implementing the optical switches necessary in this implementation.
A first router of the above kind is disclosed in the paper “A 2.56-Tb/s Multiwavelength and Scalable Switch-Fabric for Fast Packet-Switching Networks”, Yoshiharu Maeno et al., IEEE Photonics Technology Letters, Vol. 10, No 8, August 1998. It has in particular the disadvantage that a path duration cannot be selected for each packet.
A second router of the above kind is disclosed in the paper “A 160 Gbit/s throughput photonic switch for fast packet switching systems”, D. Chiaroni, D. de Bouard, C. Chauzat, J. C. Jacquinot, D. Bayart, P. Bousselet, M. Bachman and M. Sotom, Photonics In Switching, 1977, Technical Digest Series, Vol. 10, p 37–40. It has in particular the disadvantage that the number of optical switches necessary to implement it increases strongly as its capacity increases.
Each of the above two prior art routers also has the disadvantage of not limiting as much as would be beneficial noise and optical crosstalk that affect the packets at the output of the router.
One particular object of the present invention is to increase the capacity of the above kind of router and/or to limit its implementation cost whilst also limiting noise and the risk of optical crosstalk.